arm64 crashkernel fails to boot on acpi-only machines due to ACPI regions being no longer mapped as NOMAP

[takahiro.akashi@linaro.org (AKASHI Takahiro)]

On Tue, Dec 26, 2017 at 02:56:36PM +0800, Dave Young wrote:
> On 12/26/17 at 11:28am, AKASHI Takahiro wrote:
> > On Tue, Dec 26, 2017 at 09:35:17AM +0800, Dave Young wrote:
> > > [snip]
> > > > > > Well, we may be able to change pr_warn() to pr_warn_once() here, but
> > > > > > I hope that adding "numa=off" to kernel command line should also work.
> > > > > 
> > > > > Hmm, adding "numa=off" to crashkernel bootargs works, and TBH it was
> > > > > my initial thought process as well, but I am not sure if this will
> > > > > cause any regressions on aarch64 systems which use crashdump feature.
> > > > 
> > > > It should be fine since we use numa=off by default for all other arches
> > > > ie. x86, ppc64 and s390. Actually disabling numa in kdump kernel can save
> > > > mm component memory usage. 
> > > > 
> > > 
> > > Forgot to say I means in RHEL and Fedora we use numa=off for kdump..
> > 
> > Thank you for the clarification.
> > (It might be better to make numa off automatically if maxcpus == 0 (and 1?).)
> 
> Hmm, I did a quick test with qemu/kvm, kdump kernel boot without numa=off
> I'm not sure why I do not see the warning messages on x86
> machines, maybe something arm64 specific?

I didn't see the messages(i.e. "potential offnode page_structs")
on arm64 qemu (with -smp 2 -numa node -numa node).

It seems that qemu doesn't generate acpi slit(inter-node distance table).

Thanks,
-Takahiro AKASHI

> > 
> > -Takahiro AKASHI